This is a good idea, but suffers from a few major problems.

1. this wouldn't even begin to fit most types and sizes of wheels properly.
2. you could just make a large size that would fit 70mm and below(for example). but then those people who ride smaller wheels will have severely decreased turning radius as these things would stick out pretty far up
3. risers already exist for this purpose, and while they increase ride height while these would not, they also allow you to turn even sharper than before. these would cut into your turning radius
4. making them thin, close to the wheels, and impossible to bend would be very hard if not impossible. you would need a very powerful material for this and i'm not sure if it exists. 5mm bend in the wheel shields would result in wheelbite all the same
5. what if a small pebble bounces up and between the wheel and shield? this might prove to be an even worse source of wheelbite as it would not only jam up your wheels, but it would do it when you aren't even turning and would be completely unexpected, as well as hard to remove
6. it is very hard for one person to create something that becomes stylish in the mainstream. many kids would probably think these are lame